Vehicle hoist mechanism

ABSTRACT

A dump truck hoist mechanism of the &#39;&#39;&#39;&#39;scissors&#39;&#39;&#39;&#39; type has Lshaped members, depending end portions of which project down below the plane of the upper surfaces of the vehicle chassis in order to achieve a combination of (a) a comparatively wide spacing between the axis about which the two members of the mechanism are interconnected and the location at which hydraulic cylinders act on the upper member to rotate it about such axis, with resulting good leverage, and (b) a lower than normal &#39;&#39;&#39;&#39;mounting height&#39;&#39;&#39;&#39; between the vehicle and dump box chassises. A lost motion mechanism is incorporated into the pivotal connection between the dump box chassis and the upper member to facilitate the linkage.

United States Patent 1191 Seniuk VEHICLE HOIST MECHANISM Stephen PeterSeniuk, 5 Chester St., Winnipeg, Manitoba, Canada [22] Filed: Jan. 7,1972 [21] Appl. No; 216,044

[76] Inventor:

[52] US. Cl. 298/22 J [51] Int. Cl 860p l/20 [58] Field of Search 298/22J, 17.6, 17.7, 22 B,

1 1 Feb. 12, 1974 Primary ExaminerRichard J. Johnson AssistantExaminer-Reinhard J Eisenzopf [57] ABSTRACT A dump truck hoist mechanismof the scissors type has L-shaped members, depending end portions ofwhich project down below the plane of the upper surfaces of the vehiclechassis in order to achieve a combination of (a) a comparatively widespacing between the axis about which the two members of the mechanismare interconnected and the location at which hydraulic cylinders act onthe upper member to rotate it about such axis, with resulting goodleverage, and (b) a lower than normal mounting height between thevehicle and dump box chassises. A lost motion mechanism is incorporatedinto the pivotal connection between the dump box chassis and the uppermember to facilitate the linkage.

9 Claims, 15 Drawing Figures PATENTEDFEB 1 2 3.791595 smear 1 or g 1VEHICLE HOIST MECHANISM This invention relates to a hoist mechanism foruse with dump trucks or like vehicles in which a so-called box," tray orother platform is pivotally mounted on the vehicle chassis at onelocation, while at another location it can be elevated by the hoistmechanism, so as to incline the box to dump out its contents. Thispivotable part of the vehicle will be referred to hereinafter as thedump box chassis or simply box chassis. However, it is to be understoodthat this part may take the form of a simple platform with or withoutupstanding end or side walls.

More specifically, the present invention is concerned with improvementsin the so-called lever or scissors type of hoist mechanism for suchvehicles.

The principal object of the present invention is to provide improvementsin the construction of such a hoist mechanism and more particularly areduction in its required mounting height. The hoist mechanism has to bemounted in the confined space between the chassises, and its mountingheight is defined as the distance between the top surface of the vehiclechassis and the bottom of the floor of the dump box chassis. It will beapparent that the lower the mounting height the better the stability ofthe assembly, because the centre of gravity of the entire vehicle,whether loaded or not, will be lower, with less likelihood ofoverturning on rough terrain.

In vehicles fitted with conventional hoists of the scissors type, themounting height has typically been of the order of 12 inches or more.Hoists of the telescopic type have also required a minimum mountingheight of about to 12 inches, and the cam and roller type of hoist iseven less favourable in this regard, often requiring a mounting heightas high as 14 inches.

By means of the construction of the present invention, it has provedpossible to achieve a hoist mechanism having a mounting height as low as8 or even 7 inches. Moreover this reduction in the mounting height hasbeen achieved without sacrifice of other features, such as the liftingforce developed.

The manner in which this advantage is achieved is illustrated by meansof several embodiments of the invention that are illustrated in theaccompanying drawings. Such illustration is provided by way of exampleonly, and not by way of limitation of the broad scope of the invention,which latter is defined in the appended claims.

In the drawings:

FIG. 1 is a side view of a dump truck cut away to show a hoist mechanismon a relatively small scale and in its lowered position;

FIG. 2 is a view similar to FIG. 1 in the raised position;

FIG. 3 is an enlarged, vertical, central section of the hoist mechanismin lowered position, taken on the line III-III in FIG. 5;

FIG. 4 is a view similar to FIG. 3 showing the mechanism in raisedposition;

FIG. 5 is a plan view of the mechanism in its lowered.

position, taken on the line V-V in FIG. 3;

FIG. 6 is a section on the line VI-VI in FIG. 3; FIG. 7 is a section onthe line VIIVII in FIG. 3; FIG. 8 is a section on the line VIII-VIII inFIG. 5;

FIG. 9 is a side view of a hoist mechanism constructed without one ofthe essential features of the present invention;

FIG. 10 is a view of the parts of FIG. 9 at a different stage ofoperation, demonstrating the unsatisfactory mode of operation that itwould have;

FIG. 11 is a view similar to FIG. 9 but of a mechanism incorporatingsaid essential feature of the present invention;

FIG. 12 is aview similar to FIG. 10 demonstrating the manner in whichthe mechanism of FIG. 11 avoids the difficulty illustrated in FIG. 10;and

FIGS. 13 to 15 are side views illustrating fragments of variousalternative embodiments of the invention.

FIGS. 1 and2 illustrate a truck 10 having a dump box chassis 11pivotally mounted by pins 12 in the conventional manner to the truckchassis 13. A hoist mechanism 14 is connected between the vehicle andbox chassises in the manner that will now be described with reference toFIGS. 1 to 7.

The hoist mechanism 14 comprises a lower member 20 connected to thevehicle chassis l3 and an upper member 21 connected to the box chassis11, these upper and lower members being pivotally intercom nected bypins 22 so as to be movable between lowered and raised positions byhydraulic cylinders 23 that are pivotally mounted on the lower member 20by pins 24 and that have pistons 26 pivotally connected to the uppermember 21 by pins 27.

The lower member 20 is pivotally mounted on the vehicle chassis 13 bymeans of pins 28 engaging brackets 29 that are secured to mainlongitudinal members 30 of the chassis. The top surfaces of the members30 define an upper vehicle chassis plane A (FIGS. 6 and 7) above whichthe mounting height is measured.

Both the upper and lower hoist members 20 and 21 are L-shaped,consisting of main portions 20a and 21a that lie at all times above thetop chassis plane A, and depending end portions 20b and 21b whichproject down below the plane A into the space between the chassismembers 30. This L-shaping of the hoist members is an important aspectof the construction from the viewpoint of minimizing the mountingheight. The

mounting height is the distance between the plane A and a plane Bdefined by the undersurface of the floor 40 of the box chassis II. TheL-shape construction of the hoist members also allows the distancebetween the pivotal axes defined by the pins 22 and 27 respectively tobe comparatively large. The greater this distance between the axes, thegreater the upward force exerted during operation, other factors beingequal. On the other hand, the end portions 20b and 21b are able toproject downwardly below the plane A and between the members 30, whenthe mechanism is in its lowered position, without interfering with thecross sills 31 that extend at intervals transversely between thelongitudinal members 30 for ensuring the rigidity of the chassis, andwithout interfering with any other equipment that it may be convenientto locate in the space between the longitudinal members 30. The spacedapart nature of the downwardly projecting end portions 20b and 21b alsoenables them to straddle the drive shaft 60 (shown diagrammatically inFIGS. 6 and 7 only). The L-shape of the members 20 and 21 thus avoidsany need to modify the vehicle chassis structure or the mounting ofauxiliary equipment thereon.

The upper member 21 is connected to the box chassis 11 through lostmotion mechanisms that will now be described. Secured to the undersideof the floor 40 of the box chassis 11 there are a series of spaced crosssills 41 to which in turn longitudinal members 42 are secured. This isconventional construction. It is to the longitudinal members 42 that thefree end 21c of the upper member 21 is connected through the lost motionmechanisms. This free end 21c consists mainly of a transverse member(see FIG. 5) from the ends of which cylindrical projections 43 extend.These projections 43 are free to rotate in the member 21c and thusconstitute rollers. These rollers 43 engage in slots 45 formed inhousings 46 secured to respective longitudinal members 42. In thelowered position of the hoist, the rollers 43 occupy the rearward endsof the slots 45, as shown in FIGS. 1, 3, 5 and 8; while in the elevatedposition, these rollers occupy the forward ends of the slots 45, asshown in FIGS. 2 and 4, for reasons that will now be described inconnection with the diagrams of FIGS. 9

By way of preliminary explanation, FIG. 9 has been arranged to show theconditions that would exist, if the lost motion mechanisms (rollers 43and slots 45) were omitted. FIG. 9 shows the parts in loweredpositionand it has been assumed that the free end 21c of the uppermember 21 is connected to the longitudinal members 42 of the dump boxchassis by simple pivot pins 50 having no provision for lost motion.FIG. 10 demonstrates the effect of this arrangement when the cylinders23 are actuated to extend their pistons 26 and start to move themechanism towards its raised position. The initial effect of thisexpansion of the cylinders is to rotate the upper member 21anticlockwise about the pivot pins 22. This motion would, if no otherfactors were involved, move the pins 50 in an arc C described about theaxis of the pins 22 to the position shown at 50a. However, these pinscannot move to the position 50a, because they are also attached to thedump box chassis 11 which during upward movement rotates about the pins12 in an arc D, thus forcing the pins 50 to try to occupy the position50b. In other words, the box chassis 11 effectively pulls the uppermember 21 rearwardly by a distance equal to the distance betweenposition 50a and 50b. These considerations have been shown in FIG. 10with some of the dimensions slightly exaggerated in order to make thepoint clear.

This rearward pulling of the upper member 21 causes bodily rotation ofthe entire hoist mechanism in a clockwise sense about the pins 28 with asubstantial elevation of the entire forward end of the hoist mechanism.At least, this is what would happen, if it were not for the fact thatthe hoist members will interfere with the dump box. This interferencehas been illustrated diagrammatically in FIG. 10 by showing in brokenlines the upper free (left hand) corner 49 of the hoist mechanismpenetrating the floor 40 of the box. In fact the mechanism would alsointerfere with one or more of the sills 41, unless these were cut awayin the area immediately above the hoist mechanism. In practice, ofcourse, such penetration'cannot be allowed to take place, even if theforces are great enough to cause it. Assuming that they are not, whatwill happen is that either the mechanism will be severely strained or itwill bind and the box will not be elevated. In other words, the linkageis an impossible one for operation in the space available.

Some amelioration of this difficulty can be achieved by increasing theheight of the transverse sills 41, in other words by increasing themounting height, but this would be contrary to the object of the presentinvention. Moreover, should any of the sills 41 be located directlyabove the hoist mechanism, these would have to be omitted or reduced insize, which would have a general weakening effect on the rigidity of thedump box chassis and would consequently also be undesirable.

According to the invention, this difficulty is overcome by providing thelost motion mechanisms, one form of which (the rollers 43 and slots 45)is illustrated in FIGS. -1 to 8 and demonstrated geometrically in FIGS.11 and 12. FIG. 11 corresponds to FIG. 9, except that the pins 50 havebeen replaced by the rollers 43 and slots 45. When the mechanism beginsto be expanded, as shown in FIG. 12, each roller 43 is permitted to movein the are C to position 43a while its slot 45 moves in the arc D toposition 45b, until the roller reaches the forward end of the slot.During this time, there is no tendency for the upper member 21 to bepulled rearwardly and hence both hoist members remain in their lowermostpositions, except for the rotation of the upper member 21 about the pins22. By the time the rollers 43 have reached the forward ends of theslots 45 the box has risen sufficiently to provide the necessaryclearance of the box chassis from the mechanism, so that no disadvantageresults from the fact that during subsequent upward movement the rollers43 are caused to travel in the are D. Again, no attempt has been made tomake FIG. 12 dimensionally accurate, but merely to demonstrate theprinciple involved.

It might at first sight appear that the difficulty inherent in thelinkage of FIGS. 9 and 10 could be overcome by reversing the orientationof the mechanism on the vehicle, i.e. by placing the mounting pins 28forward (more remote from the pins 12) and arranging the members 20, 21to extend rearwardly towards the pins 12. This orientation would havethe effect of giving the arcs C and D a curvature in the same sense,i.e. both upwards and towards the rear. Nevertheless they would stillnot be coincident with each other, since they are described aboutdifferent axes (the axes of the pins 22 and 12 respectively), and thussome horizontal travel or lost motion would still be required. Moreover,the portion of the dump box chassis immediately overlying the upper freecorner 49 would then be nearer to the pins 12 than in the orientationillustrated, with the result that such portion would rise less for agiven angular elevation of the dump box chassis and would thereforerequire the mechanism to reach a more expanded condition before theelevation of the dump box chassis became sufficient to avoid any furtherdifficulty of inter ference between the upper free corner 49 of themechanism and such overlying portion.

It will be noted from FIG. 8 that the upper surface 48 of each slot 45is inclined to the horizontal. This is to avoid another factor thatwould otherwise tend to force the forward end of the mechanism upwardly.As the mechanism begins to elevate the box chassis, the weight of thebox and its contents bears down on each roller 43 through the surface48. This force is applied normal to the surface 48, i.e. in thedirection of the arrow B in FIG. 8. It will be noted that the line ofaction of the force E passes to the left (forwardly) of the axis definedby the pins 28. As a result, the effect of this force is to try torotate the hoist mechanism bodily in a counterclockwise direction aboutthe pins 28; in other words, to hold the forward ends 20b and 21b of thetwo members firmly downward in their lowermost positions. If the slots45 had been formed with horizontal bearing surfaces 48, this downwardforce E would have acted rearwardly of the axis of the pins 28, whichwould have produced a clockwise moment on the whole assembly tending toforce up the left hand ends 20b and 21b against the underside of thebox. While in this case the linkage would not be an impossible one, theforces that would exist could be damaging.

In the event that the axis of the rollers 43 is located forwardly of theaxis of the pins 28, as shown in the alternative construction of FIG.13, there no longer remains any need to incline the slots 45 upwardlyand forwardly and they can conveniently be arranged to extend trulyhorizontally.

FIGS. 14 and show further alternative constructions of lost motionmechanisms. In FIG. 14, each transverse end of the free end 21c of themember 21 is pivotally connected by a pin 51 to one end of a link 52,the other end of which is pivotally connected by a pin 53 to a fixedbracket 54 secured to the underside of the box chassis 11. Duringinitial operation of this arrangement, the pins 51 are free to travel inthe are C, while the pins 53 can travel in the arc D, the links 52rotating counterclockwise during this time. The limit of this rotationis determined by the balance of forces. However, the link 52 as soon asit becomes slightly inclined to the vertical will transmit somehorizontal rearward force from the bracket 54 to the pins 51, thustending to elevate the front end 49 of the mechanism 14 causing thelatter to exert some upward pressure on the box chassis 11; but far lessthan in the situation depicted in FIG. 10, by virtue of the lost motioneffect of the links 52. For this reason the linkage arrangement of FIG.14 is less preferred than the slot arrangements of FIGS. 1 to 13 or theslider arrangement of FIG. 15.

FIG. 15 shows an alternative embodiment in which the lost motion effectis achieved by connecting each transverse end of the free end 21c by apin 55 to a slider 56 mounted to slide along a rod 57 that is firmlymounted between bracket members 58 secured to the underside of the boxchassis 11. This arrangement again permits the pins 55 to travel in thearc C while the rod 57 travels in the are D. In the embodiment shown inFIG. 15, the pins 55 are located slightly forwardly of the pins 28, sothat the downward forces will tend to have a counterclockwise (i.e.depressing) action on the hoist mechanism as a whole. In the event thatthe construction is such that it is moreconvenient to arrange the pinsrearwardly of the pins 28, then the rod 57 should preferably be inclinedin a manner analogous to the inclination of the slots 45, in order thatthe force normal to the longitudinal axis of the rod 57 will still passto the left (forwardly) of the axis of the pins 28.

The location of the lost motion in the connection between the hoistmechanism and the dump box chassis is preferred, because it provides afirm mounting of the hoist mechanism on the vehicle; but nevertheless itis possible to provide essentially the same lost motion effect withessentially the same advantages in the avoidance of interference, bylocating the lost motion mechanisms in the pivotal connections betweenthe hoist mechanism and the vehicle chassis, i.e. at the pins 28. Theentire hoist mechanism would then be subject to some front to reardisplacement during the initial stages of elevation. The invention inits broad scope thus includes this alternative.

Similarly, while in the embodiment of FIGS. 1 to 8, the slots 45 havebeen shown mounted on the chassis and the cooperating members (rollers43) which engage them are located on the hoist mechanism, thisorientation can be reversed, if desired, to locate the slots on thehoist mechanism and the cooperating members on the chassis. Thisalternative is thus also within the scope of the invention.

I claim:

1. A hoist mechanism for mounting in a confined space between a vehiclechassis having an upper surface defining a first horizontal plane and adump box chassis overlying said vehicle chassis and being connectedthereto about a first axis to be pivotable in a first are between alowered position defining a second horizontal plane and a tilted, raisedposition; said mechanism comprising a. an elongate lower member and anelongate upper member overlying the lower member in a generally paralleland nesting orientation thereto for enabling mounting of said members insaid confined space,

b. means pivotally interconnecting first ends of said members to definea second axis,

c. first connecting means for pivotally connecting a second end of saidlower member to the vehicle chassis to rotate about a third axis remotefrom said second axis,

d. second connecting means for pivotally connecting a second end of saidupper member to the dump box chassis to rotate about a fourth axisremote from the second axis and generally overlying the third axis,

e. and fluid-pressure-operated means extending between said members forrotating said upper member relative to the lower member so that saidsecond end of the upper member travels in a second are described aboutsaid second axis,

f. wherein one of said connecting means (0) and (d) includes lost motionmeans enabling generally horizontal relative movement for a limiteddistance between a selected one of said chassises and the second memberend connected to such selected chassis by said one connecting means, toenable said upper member to move in said second arc during initialupward rotation of said dump box chassis notwithstanding rotation of thelatter in said first arc,

g. wherein said lost motion means comprise a first part in the form ofat least one slot extending generally in the horizontal direction and asecond part in the form of a member cooperating with each said slot, oneof said parts being mounted on said selected chassis and the other ofsaid parts being mounted on the second member end whereby to provideboth a horizontal lost motion effect and a pivotal connection.

2. A hoist mechanism according to claim 1, wherein said selected chassisis the dump box chassis.

3. A hoist mechanism according to claim 2, wherein said slot is soinclined that a generally downward force exerted by said slot on itscooperating member extends on the side of said third axis towards saidsecond axis.

4. A hoist mechanism according to claim 1, wherein each of said membershas a main portion extending horizontally between the chassises abovesaid first plane and a depending end portion extending below said firstplane, and wherein said second axis extends through said depending endportions.

5. A hoist mechanism according to claim 4, wherein thefluid-pressure-operated means extend between a location on the lowermember in the vicinity of said third axis and a location on the uppermember above said second axis and substantially spaced therefrom.

6. A hoist mechanism for mounting in a confined space between a vehiclechassis having an upper surface defining a horizontal plane and a dumpbox chassis overlying said vehicle chassis and pivotally connectedthereto; said mechanism comprising a. elongate, upper and lower membershaving main portions extending horizontally in said confined space abovesaid plane and depending end portions projecting below said plane,

b. means pivotally interconnecting said depending end portions about afirst axis,

0. means pivotally connecting an end of the main portion of the lowermember remote from its depending end portion to the vehicle chassisabout a second axis,

d. means connecting an end of the main portion of the upper memberremote from its depending end portion to the dump box chassis,

e. and fluid-pressure-operated means extending between said members foreffecting rotation of the upper member about said first axis,

f. said connecting means ((1) comprising at least one generallyhorizontal slot located in the dump box chassis and a member cooperatingwith said slot mounted on said remote end of the upper member whereby toprovide both a horizontal lost motion and a pivotal connection betweenthe dump box chassis and the upper member.

7. A hoist mechanism according to claim 6, wherein said slot is soinclined that a generally downward force exerted by said slot on thecooperating member extends on the side of said second axis towards saiddepending end portions.

8. in a vehicle having a main vehicle chassis and a dump box chassispivotally connected thereto, a hoist mechanism mounted between andpivotally connected to said chassises, said mechanism comprising a.elongate, upper and lower members having .main

portions extending horizontally between said chassises and depending endportions projecting below a plane defined by an upper surface of thevehicle chassis,

b. pin means pivotally interconnecting said depending end portions,

c. fluid-pressure-operated means extending between said members foreffecting rotation of the upper member about said pin means andconsequent elevation of the dump box chassis,

(1. said pivotal connection of the hoist mechanism to the chassisesincluding lost motion mean for enabling said upper member to rotatesolely about said pin means during initial upward rotation of the dumpbox chassis on the vehicle chassis,

e. wherein said lost motion means comprise at least one generallyhorizontal slot located in the dump box chassis and a member cooperatingwith said slot mounted on the upper member of the hoist mechanism.

9. In a vehicle having a main vehicle chassis and a dump box chassispivotally connected thereto, a hoist mechanism mounted between andpivotally connected to said chassises, said mechanism comprising a.elongate, upper and lower members having main portions extendinghorizontally between said chas sises and depending end portionsprojecting below a plane defined by an upper surface of the vehiclechassis,

b. pin means pivotally interconnecting said depending and portions,

c. fluid-pressureoperated means extending between said members foreffecting rotation of the upper member about said pin means andconsequent elevation of the dump box chassis,

d. said pivotal connection of the hoist mechanism to the chassisesincluding lost motion means for enabling said upper member to rotatesolely about said pin means during initial upward rotation of the dumpbox chassis on the vehicle chassis,

e. wherein said depending end portions are arranged to extend below thelevel of a drive shaft extending along said vehicle chassis whilestraddling said shaft.

1. A hoist mechanism for mounting in a confined space between a vehiclechassis having an upper surface defining a first horizontal plane and adump box chassis overlying said vehicle chassis and being connectedthereto about a first axis to be pivotable in a first arc between alowered position defining a second horizontal plane and a tilted, raisedposition; said mechanism comprising a. an elongate lower member and anelongate upper member overlying the lower member in a generally paralleland nesting orientation thereto for enabling mounting of said members insaid confined space, b. means pivotally interconnecting first ends ofsaid members to define a second axis, c. first connecting means forpivotally connecting a second end of said lower member To the vehiclechassis to rotate about a third axis remote from said second axis, d.second connecting means for pivotally connecting a second end of saidupper member to the dump box chassis to rotate about a fourth axisremote from the second axis and generally overlying the third axis, e.and fluid-pressure-operated means extending between said members forrotating said upper member relative to the lower member so that saidsecond end of the upper member travels in a second arc described aboutsaid second axis, f. wherein one of said connecting means (c) and (d)includes lost motion means enabling generally horizontal relativemovement for a limited distance between a selected one of said chassisesand the second member end connected to such selected chassis by said oneconnecting means, to enable said upper member to move in said second arcduring initial upward rotation of said dump box chassis notwithstandingrotation of the latter in said first arc, g. wherein said lost motionmeans comprise a first part in the form of at least one slot extendinggenerally in the horizontal direction and a second part in the form of amember cooperating with each said slot, one of said parts being mountedon said selected chassis and the other of said parts being mounted onthe second member end whereby to provide both a horizontal lost motioneffect and a pivotal connection.
 2. A hoist mechanism according to claim1, wherein said selected chassis is the dump box chassis.
 3. A hoistmechanism according to claim 2, wherein said slot is so inclined that agenerally downward force exerted by said slot on its cooperating memberextends on the side of said third axis towards said second axis.
 4. Ahoist mechanism according to claim 1, wherein each of said members has amain portion extending horizontally between the chassises above saidfirst plane and a depending end portion extending below said firstplane, and wherein said second axis extends through said depending endportions.
 5. A hoist mechanism according to claim 4, wherein thefluid-pressure-operated means extend between a location on the lowermember in the vicinity of said third axis and a location on the uppermember above said second axis and substantially spaced therefrom.
 6. Ahoist mechanism for mounting in a confined space between a vehiclechassis having an upper surface defining a horizontal plane and a dumpbox chassis overlying said vehicle chassis and pivotally connectedthereto; said mechanism comprising a. elongate, upper and lower membershaving main portions extending horizontally in said confined space abovesaid plane and depending end portions projecting below said plane, b.means pivotally interconnecting said depending end portions about afirst axis, c. means pivotally connecting an end of the main portion ofthe lower member remote from its depending end portion to the vehiclechassis about a second axis, d. means connecting an end of the mainportion of the upper member remote from its depending end portion to thedump box chassis, e. and fluid-pressure-operated means extending betweensaid members for effecting rotation of the upper member about said firstaxis, f. said connecting means (d) comprising at least one generallyhorizontal slot located in the dump box chassis and a member cooperatingwith said slot mounted on said remote end of the upper member whereby toprovide both a horizontal lost motion and a pivotal connection betweenthe dump box chassis and the upper member.
 7. A hoist mechanismaccording to claim 6, wherein said slot is so inclined that a generallydownward force exerted by said slot on the cooperating member extends onthe side of said second axis towards said depending end portions.
 8. Ina vehicle having a main vehicle chassis and a dump box chassis pivotallyconnected thereto, a hoist mechanism mounted between and pivotallyconnected to said chassises, said mechanism comprising a. elongate,upper aNd lower members having main portions extending horizontallybetween said chassises and depending end portions projecting below aplane defined by an upper surface of the vehicle chassis, b. pin meanspivotally interconnecting said depending end portions, c.fluid-pressure-operated means extending between said members foreffecting rotation of the upper member about said pin means andconsequent elevation of the dump box chassis, d. said pivotal connectionof the hoist mechanism to the chassises including lost motion mean forenabling said upper member to rotate solely about said pin means duringinitial upward rotation of the dump box chassis on the vehicle chassis,e. wherein said lost motion means comprise at least one generallyhorizontal slot located in the dump box chassis and a member cooperatingwith said slot mounted on the upper member of the hoist mechanism.
 9. Ina vehicle having a main vehicle chassis and a dump box chassis pivotallyconnected thereto, a hoist mechanism mounted between and pivotallyconnected to said chassises, said mechanism comprising a. elongate,upper and lower members having main portions extending horizontallybetween said chassises and depending end portions projecting below aplane defined by an upper surface of the vehicle chassis, b. pin meanspivotally interconnecting said depending end portions, c.fluid-pressure-operated means extending between said members foreffecting rotation of the upper member about said pin means andconsequent elevation of the dump box chassis, d. said pivotal connectionof the hoist mechanism to the chassises including lost motion means forenabling said upper member to rotate solely about said pin means duringinitial upward rotation of the dump box chassis on the vehicle chassis,e. wherein said depending end portions are arranged to extend below thelevel of a drive shaft extending along said vehicle chassis whilestraddling said shaft.